failed attitude indicator:
I would think that this plane had at least two attitude indicators. One in front of the pilot, one in front of the copilot's seat and perhaps a third standby instrument.
I can even imagine a possible installation of EFIS type instruments in front of the pilot.
BUT, conflicting information can be a real brain challenge...which one or two are correct? And then, having the courage to use the proper one and ignore the other? Covering the bad instrument with a piece of paper would be one of the first things I would do (piece of paper, spit on it and slop it on the bad one).
My feeling is that confusion was in the mind of the pilot. Perhaps confusion from more than one source. Perhaps an over dependence on auto pilot and lack of familiarity with unusual attitude recovery. Perhaps pitot tube was iced over giving eroneous air speed information?
To get to 3000' would indicate to me that the wings were ok for takeoff and climbout. (in terms of ice)
Vertigo, illusions, etc. may play a part. The bit about taxi route concerns me quite a bit. Confusion, subtle incapacitation can be deadly.